Kaunas Fortress was a colossal military defensive complex encircling the city, with ten forts built by the Russians 1882-1915 to protect their empire from the growing power of Germany. But when World War I came, after 11 days of assault the forts surrendered; so the Fortress had impeded the enemy advance but proved far from impregnable. From 1920 much of it was demolished or turned over to other state use. The Ninth Fort was the best preserved and was put to horrific use during the Nazi occupation of 1941-44. You enter via the Exposition of Occupations which has the ticket office, and documents the wartime terrors, and the ensuing Soviet terror under Stalin. You then visit the 9th Fort and the 32m high memorial to the victims; the fort tunnels can only be seen by special tour.